Preclinical testing requires performance of laboratory and animal studies to determine the biological activity of the drug candidate against the targeted disease as well as drug safety. These tests take at least three years in mammalian models and only a very small number of compounds proceed to human testing. The cell culture system is currently used as an in vivo assay to evaluate molecular and regulatory effects within cells for drug discovery, however, cells lacking intact metabolic machinery often experience fewer toxic effects compared to animal models. This SBIR aims to develop the zebrafish as an inexpensive animal model for drug toxicity testing. Using zebrafish embryos, this SBIR will develop a comprehensive toxicity prescreening system comprised of a low density array and complementary visual assays to examine gene expression, cellular damage and morphological defects in response to drug treatment. The proposed zebrafish assays will help to reduce drug development costs by reducing the number of compounds entering preclinical mammalian and human testing. PROPOSED COMMERCIAL APPLICATION: By providing a rapid and inexpensive toxicity prescreening system, the zebrafish assays will facilitate the drug development process for a variety of diseases, including cancer and heart disease.